Citing possible risks to young children, Health Canada recently banned plastic baby bottles made from bisphenol A and is proposing to ban toys containing six types of phthalates, best known as the rubber duck chemical.
Singling out babies and toddlers for special protection against harmful chemicals is a good idea because infants, with their rapidly growing bodies and unique exposure patterns, can be more vulnerable to dangerous chemicals than are most adults.
But a question has arisen about Health Canada's actions: If young children shouldn't come into contact with the two chemicals, what about pregnant women and their fetuses, which are even more susceptible to harmful compounds, especially those with hormonal impacts, like these man-made substances?
Bisphenol A is an estrogen mimic, meaning exposure gives an extra hit of the female hormone, while phthalates interfere with testosterone production, reducing levels of the crucial male hormone.
During fetal development, in particular, humans are extremely sensitive to sex hormones. Everything from genital development to brain organization is choreographed by specific levels of these hormones circulating in the womb at precise points in the pregnancy. If levels are skewed by synthetic chemicals, there is the risk of irreversible, life-long changes occurring.
"Pregnant women and the fetus are in fact the greatest target group for all of these chemicals," says Frederick vom Saal, a professor at the University of Missouri and one of the leading researchers in the U.S. investigating bisphenol A, or BPA as it is also known.
Health Canada needs "to now take the next logical step" and consider wider restrictions on the chemicals to reduce exposures in pregnant women, contends Dr. vom Saal. The agency shouldn't assume "that by just targeting protections for newborns they've done enough."
Although Health Canada took action against the two chemicals to protect children, the most provocative research on both compounds has been done on pregnant rodents and on their pups during early neonatal life, the period that corresponds to the last part of gestation in humans. Because conducting experiments on pregnant women would be unethical, these animal laboratory tests are designed to flag possible harmful effects on people.
Such experiments have found dramatic results, including enlarged prostates, skewed mammary ducts that in women would translate into increased breast cancer risk, and the feminization of male genitals.
Safeguards for pregnant women are needed, agreesanother top researcher in the field, Shanna Swan, director of the Center for Reproductive Epidemiology at the University of Rochester's school of medicine, and an authority on phthalates. While children are sensitive to the chemicals, they're "not as sensitive as the fetus. There is no question about that," says Dr. Swan.
Dr. Swan has published a study finding that women who have higher levels of phthalates during pregnancy give birth to boys with a slightly shorter distance from the start of their genitals to the anus, mirroring a discovery made in male rodents exposed to the chemical. In rodents, the shrinkage is viewed as feminizing the male genital tract, but the effect occurred at far higher doses than what is found in people exposed to the chemicals.
Nonetheless, because there is animal evidence of harm during gestation, Dr. Swan says "we should assume until proven otherwise that it's reproductively toxic to humans."
Health Canada said it is monitoring research on the chemicals, but it believes the weight of evidence does not yet warrant measures to reduce exposures by pregnant women.
"Health Canada will take appropriate action if a risk to human health is identified," it said in an e-mailed response to questions.
But the federal agency has begun several studies on pregnant women and their babies to see whether the animal research is onto something, and has ordered up research to see if the genitals of newborns have been affected by their mothers' exposure to the two chemicals.
Last month , for instance, it posted a notice indicating that it has asked a McMaster University researcher to study pregnant women to find out whether BPA affects the anogenital distance in their babies. It has a similar study on phthalates to try to duplicate Dr. Swan's findings.
In human babies, as in rodent pups, males typically have a larger distance from the anus to the genitals than females, and it is likely that anything reducing the sex difference would be hormonal in nature.
The chemical industry said it welcomes the research and predicted its products will get a clean bill of health. "We are confident that the levels of bisphenol A that will be found will be extremely low and we think it's unlikely that any health effects will be observed," said Steven Hentges, spokesman for the American Chemistry Council.